"When it comes to multiway extension leads - people in the UK are sometimes told it's bad to "overload" sockets but have only a vague understanding of what that means, so some people are reluctant to use them."

To be fair, most people work on the assumption that if the consumer unit doesn't complain, then it is fair game. They are relying on modern standards, which nowadays is quite reasonable. I suppose it is good that we can nowadays rely on standards.

However, I have lived in a couple of houses with fuse wire boards, one of which the previous occupants put in a nail for a circuit that kept burning out.

Good practice is to put a low rated fuse - eg 5A (red) into extension leads for most devices. A tuppence part is easy and cheap to replace but if a few devices not involved with room heating/cooling blow a 5A fuse, you need to investigate. A hair dryer, for example, should not blow a 5A fuse.